One More Poliovirus Strain Now Eradicated

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One strain of the virus that causes polio has likely been
eradicated worldwide, according to a new report.

For two years now, there have been no new reports of polio caused
by this strain, called poliovirus type 3, according to
researchers from World Health Organization (WHO) and Centers for
Disease Control and Prevention (CDC).

The possible eradication of the poliovirus type 3 would be a
"historic milestone" for global polio eradication efforts, the
researchers said in their report released today (Nov. 13).

The world is not yet rid of polio. There are three strains of the
virus, and type 1 is still actively being transmitted in three
countries: Nigeria, Pakistan and Afghanistan. Transmission of
poliovirus type 2 has been stopped since 1999. [ 5 Scariest Disease Outbreaks of the Past
Century ]

Poliovirus causes polio, or poliomyelitis, as the condition is
properly called. The disease is a highly contagious and incurable
infection of the nervous system, but can be prevented
by vaccination. In the 1980s, the virus killed or paralyzed
about 350,000 people worldwide each year. But since the WHO's
Global Polio Eradication Initiative was launched in 1988,
the number of cases has fallen by over 99 percent.

Still, because the type 1 poliovirus is spreading in three
countries, the disease continues to pose a threat to any
polio-free region in the world where vaccination levels
are not sufficiently high, according to the World Health
Organization.

Poliovirus type 1 is the most virulent of all strains of this
virus, causing illness in 1 out of every 200 people it infects.
Type 3 sickens about 1 in 2,000 people it infects.

The last case of polio caused by the type 3 strain of the virus
was an 11-month-old infant in Nigeria, who became paralyzed on
Nov. 10, 2012, according to WHO. Since then, no other cases have
been reported, and the virus hasn't shown up in lab tests
conducted by the organization's polio surveillance team. Still,
continued surveillance will look at whether poliovirus type 3 is
in fact fully stopped.

If confirmed, the successful eradication of poliovirus type 3
shows that implementing WHO's vaccination plans in the three
remaining countries will also stop
the spread of poliovirus type 1, the researchers said.